To count how many instructions a line of code executes:
(dbx) ... # get to the line in question (dbx) stop step -instr -count infinity (dbx) step ... (dbx)status (3) stop step -count 48/infinity # 48 instructions were executed
If the line you are stepping over makes a function call, you end up counting those as well. You can use the next event instead of step to count instructions, excluding called functions.